The present invention relates to a method for providing a chrome finish on a substrate, and more particularly, the present invention relates to a chroming process that is environmentally-friendly and that produces a rich, bright, reflective chrome coating traditionally desired by the automotive, furnishing, and other industries. The present invention also relates to a coated substrate having a chrome finish.
Conventionally, nickel/chromium and/or chromium is electroplated on aluminum and steel parts and provides an industry standard for a rich, reflective, chrome finish widely accepted, desired, and used in the automotive, furnishing and like industries. Chrome plating requires the use of hazardous solutions and bi-products that present numerous environmental issues and problems. In addition, since chromium is a very hard material, it is well known that a layer of material having high chromium content that is plated on a substrate tends to fracture or “craze” when the substrate is flexed and/or thermally expanded.
U.S. Pat. No. 6,399,152 B1 issued to Goodrich discloses a vacuum metalization process that can be used to apply chrome coatings on aluminum and steel substrates and that addresses the above referenced environmental concerns. The process requires vapor deposition of a nickel/chromium layer on a substrate, and thereafter, the separate vapor deposition of a chromium layer on the pre-deposited nickel/chromium layer. The result is a substrate having a decorative chrome finish that is of a color desired, and in some cases required, by the automotive industry. The coating is believed to provide good resistance to corrosion, and the process can be practiced without the environmental problems experienced in connection with plating processes. However, as stated above, layers of material having high chromium content tend to fracture or “craze” when the underlying substrate is flexed and/or thermally expanded. For example, see U.S. Pat. No. 4,374,717 issued to Drauglis et al. which discloses a method of sputtering a bright metal thin-layer finish on a molded plastic item, such as an automotive trim part. On column 1, lines 34–38, the Drauglis patent acknowledges the concern that thermal cycling can lead to delamination of the coating and that flexing a substrate can cause a sputtered layer to crack and peel.
U.S. Pat. No. 4,535,024 issued to Parker discloses a vapor deposited “black chrome” finish on external automotive trim parts, and U.S. Pat. No. 4,183,975 issued to Sidders and U.S. Pat. No. 4,131,975 issued to Blum et al. disclose sputtered coatings that provide the appearance of bright chromium metal traditionally used in the automotive industry and that possess the requisite corrosion and abrasion resistance for various automotive trim components. U.S. Pat. No. 6,068,890 issued to Käumle et al., U.S. Pat. No. 5,284,679 issued to Eisfeller et al., and U.S. Pat. No. 4,407,871 issued to Eisfeller disclose methods for applying high-stress resistant gloss coatings to articles, such as vehicle wheels, rims, bumpers, and grills, and U.S. Pat. No. 5,558,909 issued to Poliquin et al. discloses an apparatus and method for vapor depositing a metal layer on complex-shaped articles, such as automotive wheels and rims. U.S. Patent Application Publication No. 2004/0154539 A1 and U.S. Pat. No. 5,773,154 issued to Takada, U.S. Pat. No. 5,656,335 issued to Schwing, U.S. Pat. No. 6,326,057 B1 issued to Das et al., U.S. Pat. No. 3,801,357 issued to Baldi, U.S. Pat. No. 3,922,396 issued to Speirs et al., and U.S. Pat. No. 4,382,976 issued to Restall disclose other types of coatings and processes.
While the coatings and processes disclosed in the above referenced patents and published application may function in a satisfactory manner for their intended purposes, there remains a need for a environmentally-friendly process for providing a chrome finish on a substrate. The chrome finish produced by the process should have superior material properties and provide a desired chrome appearance traditionally accepted in the automotive industry.